RFRXD0420T-I/LQ Microchip Technology, RFRXD0420T-I/LQ Datasheet - Page 18

• Manufacturer Part Number: RFRXD0420T-I/LQ
• Description: IC RCVR 315/433MHZ ASK/FSK32LQFP
• Manufacturer: Microchip Technology

Specifications of RFRXD0420T-I/LQ

• Frequency: 300MHz ~ 450MHz
• Sensitivity: -106dBm
• Data Rate - Maximum: 80 kbps
• Modulation Or Protocol: ASK, FM, FSK
• Applications: Home Automation, Remote Sensing, RKE
• Current - Receiving: 9.2mA
• Data Interface: PCB, Surface Mount
• Antenna Connector: PCB, Surface Mount
• Voltage - Supply: 2.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 32-LQFP
• For Use With: DV164102 - KIT DEV RFPICKIT KIT 1
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Memory Size: -

rfRXD0420/0920
3.3
Figure 3-13 illustrates an example FSK application
circuit.
3.3.1
As mentioned in the Section 3.1 above, IF filter band-
width selection is a function of:
• modulation (ASK, FSK or FM)
• signal bandwidth
• frequency and temperature tolerances of the
The occupied bandwidth of binary FSK signals is 2
times the peak frequency deviation plus 2 times the
signal bandwidth. For example, if the data rate is 2400
bits per second Manchester encoded, the signal band-
width is 4800 baud or 1200 Hz, and if the peak
frequency deviation is 24 kHz, the minimum bandwidth
of the IF filter is:
Add to this value the frequency and temperature
tolerances of the transmitter and receiver components.
FSK signals are more sensitive to group delay varia-
tions of the IF filter. Therefore, a filter with a low group
delay variation should be used. As an alternative, a
filter with wider than required bandwidth can be used
because the group delay variation in the center of the
bandpass will be relatively constant.
3.3.2
The demodulator (DEMOD) section consists of a phase
detector (MIXER2) and amplifier creating a quadrature
detector (also known as a phase coincidence detector)
to demodulate the IF signal in FSK and FM modulation
applications. The in-phase signal comes directly from
the output of the IF limiting amplifier to MIXER2. The
quadrature signal is created by an external tuned circuit
from the output of the IF limiting amplifier (2IF
15) AC-coupled to the MIXER2 DEM
3.3.2.1
The external tuned circuit can be constructed from
simple inductor-capacitor (LC) components. This type
circuit produces and excellent output. However, one of
the elements (L or C) must be tunable. Figure 3-14
illustrates an example LC discriminator circuit using a
tunable capacitor. A similar circuit with a tunable induc-
tor is also possible. Resistor R1 = 4.7 kΩ reduces the
Q of the circuit so that frequency deviations of up to 75
kHz can be demodulated.
DS70090A-page 18
transmitter and receiver components
IF BW
IF BW
IF FILTER CONSIDERATIONS
FSK DETECTOR
Frequency Shift Keying (FSK)
LC Discriminator
min
min
= (2 x 2400) + (2 x 24000)
= 52800 Hz
IN
(Pin 16) input.
OUT
, Pin
Preliminary
FIGURE 3-14: LC DISCRIMINATOR
3.3.2.2
A no-tune solution can be constructed with a ceramic
discriminator. Figure 3-15 illustrates an example
ceramic discriminator circuit.
The ceramic discriminator acts as a parallel tuned
circuit at the IF frequency (for example, 10.7 MHz). The
parallel capacitor C3 tunes the ceramic resonator. The
high Q of this circuit enables higher output of the detec-
tor for small frequency deviations. However, smaller
frequency
tolerances at the transmitter and receiver.
In order to detect wider deviation or off-frequency
signals, the detector bandwidth has to be increased.
This can be accomplished by reducing the Q of the
tuned circuit. One method is to parallel a resistor
across the ceramic discriminator. A second is to
increase the value of the coupling capacitor C1
increasing the load on the detector. The result of
reducing the Q of the discriminator will be that the
detector output will be smaller.
FIGURE 3-15: CERAMIC DISCRIMINATOR
Ceramic Discriminator
15
deviations
15
1.0 pF
EXAMPLE CIRCUIT
EXAMPLE CIRCUIT
C1
1.0 pF
C1
16
CERAMIC DISCRIMINATOR
16
 2003 Microchip Technology Inc.
C2
680 pF
require
C2
680 pF
0-56 pF
4.7 kΩ
3.3 µH
R1
C3
L1
10-12 pF
F1
C3
better
frequency